Preparation of polystyrene-based activated carbon spheres with high surface area and their adsorption to dibenzothiophene

Polystyrene-based activated carbon spheres (PACS_K) with high surface area were prepared through KOH activation. Effects of the carbonization temperature and the ratio of KOH to carbon spheres (CS) on the textural structure, hardness and yield of the resultant PACS_K were studied, and their adsorption to dibenzothiophene (DBT) were investigated. The as-prepared PACS_K exhibited a high surface area (up to 2022 m²/g), large total pore volume (≥ 0.78 cm³/g), superior mechanical hardness and high adsorption capacity (ca. 153 mg/g). With the increase of the KOH/CS ratio from 2:1 to 4:1, the surface area, total pore volume, volume of micropores, and volume of mesopores, increase, whereas the volume of small-micropores (< 0.8 nm) decreases from 0.36 to 0.31 cm³/g. The adsorption capacity has a good linear correlation with the volume of small-micropores rather than the surface area. In addition, the large quantity of acidic oxygen-containing groups of PACS_K may also be responsible for their higher adsorption capacity and selectivity of DBT. The PACS_K saturated by DBT can be regenerated by a washing process in a shaking bath or using ultrasonic with toluene at 80 °C.     

Synthesis of mesoporous carbons for supercapacitors from coal tar pitch by coupling microwave-assisted KOH activation with a MgO template

Mesoporous carbons (MCs) for supercapacitors were prepared from coal tar pitch by a microwave-assisted one-step process coupling the potassium hydroxide (KOH) activation and magnesium oxide (MgO) template. MCs were characterized by scanning electron microscope and X-ray diffraction. The results show that the specific surface area (S_BET), micropore volume and specific capacitance of MCs made by microwave heating as well as the energy density of MC capacitors pass through a maximum with increasing mass of MgO and the relative mass ratio of KOH/pitch. The S_BET of MCs varies from 1003 to 1394 m²/g. The S_BET and total pore volume of MC and microporous carbon made by microwave heating are bigger than that made by conventional heating. Under optimum conditions with the masses of coal tar pitch, MgO, KOH at 9 g, 12 g, 6 g, and the microwave power at 600 W, MC (MC_9-12-6) made at 30 min heating time shows a high specific capacitance of 224 F/g in 6 M KOH aqueous electrolyte after 1000 cycles. The results have shown that microwave-assisted rapid KOH activation coupled with the MgO template is an efficient one-step approach to the preparation of low cost yet high performance MCs for supercapacitors.     

Pore structures of multi-walled carbon nanotubes activated by air, CO2 and KOH

Multi-walled carbon nanotubes (MWNTs) synthesized by the catalytic decomposition of benzene were activated by KOH, CO₂ or air. The adsorption isotherms of the activated MWNTs were analyzed and their pore size distributions were obtained. The results showed that the specific surface areas of the MWNTs activated by KOH, CO₂ and air were increased to 785 m²/g, 429 m²/g and 270 m²/g, respectively. The MWNTs activated by KOH were rich in micropores and mesopores, especially high mesopores having volumes up to 1.04 cm³/g. The CO₂-activated MWNTs also had many micropores while the air-activated MWNTs had a much smaller micropore volume. The morphologies of the activated MWNTs were examined by transmission electron microscopy and high resolution transmission electron microscopy, and the activation mechanisms were discussed.     

Formation of the pore structure of brown coal upon thermolysis with potassium hydroxide

The pore-structure characteristics of active carbons prepared by the thermolysis (800°C) of brown coal impregnated with potassium hydroxide were studied. The dependence of the specific surface area, total pore volume, micropore volume, micropore fraction, and micropore size distribution on the KOH/coal weight ratio R _KOH ≤ 1.0 g/g was found. Condensation processes with the formation of a low-porosity material were predominant at low ratios of R _KOH ≤ 0.1 g/g. The development of a micropore structure was observed at R _KOH ≥ 0.1 g/g, and it increased as R _KOH was increased to 1.0 g/g. It was hypothesized that pore formation was due to the thermally initiated reactions of the structural fragments of coal with KOH molecules, which occurred within the framework of coal.     

Alkaline activation of the donbass coals of different ranks

The effect of the rank of coal (C ^daf = 80?95.2%) on the yield and characteristics of activated carbons prepared under the conditions of alkaline activation (800°C, 1 h, Ar) at KOH/coal ratios of 1 g/g was studied. Under these conditions, the ability of coals to form porous materials decreased in the metamorphic series. Grade D coal (C ^daf = 80%) exhibited a maximum activation ability to form a material with S _BET = 1560 m²/g, V _Σ = 0.71 cm³/g, and V _mi = 0.51 cm³/g. A minimum activation ability was found in anthracite (C ^daf = 95.2%), which forms activated carbon with poorly developed porosity (S _BET = 306 m²/g, V _Σ = 0.15 cm³/g, and V _mi = 0.11 cm³/g).     

Hierarchical porous carbon obtained from animal bone and evaluation in electric double-layer capacitors

Animal bone, an abundant biomass source and high volume food waste, had been converted into a hierarchical porous carbon in a simple two-step sustainable manner to yield a highly textured material. The structures were characterized by nitrogen sorption at 77 K, scanning electron microscopy and X-ray diffraction. The electrochemical measurement in 7 M KOH electrolyte showed that the porous carbon had excellent capacitive performances, which can be attributed to the unique hierarchical porous structure (abundant micropores with the size of 0.5–0.8 and 1–2 nm, mesopores and macropores with the size of 2–10 and 10–100 nm), high surface area (S_BET = 2157 m²/g) and high total pore volume (V_t = 2.26 cm³/g). Its specific capacitance was 185 F/g at a current density of 0.05 A/g. Of special interest was the fact that the porous carbon still maintained 130 F/g even at a high current density of 100 A/g.     

Preparation of Activated Carbons from Tobacco Stems by Potassium Hydroxide Activation and Phosphine Adsorption

Activated carbon preparation from tobacco stems by KOH activation at different activation temperatures and KOH/char mass ratios were investigated in this study. The effects of preparation parameters on activated carbon pore structure, morphometrics, microcrystallinities, and surface functional groups were characterized by N₂ adsorption, SEM, XRD, and FTIR technologies, respectively. The optimum preparation condition of activated carbon was activation temperature of 850°C, and KOH/char mass ratio of 2. Under this condition, the BET surface area of 2215 m²/g, and the pore volume of 1.343 cm³/g can be obtained. Prepared activated carbon showed clearly honeycomb holes, and a predominated amorphous structure. With increase of activation temperature and KOH/char mass ratio, decrease of surface oxygen functional group, and aromatization of the carbon structure was found. The activated carbon was subject to PH₃ purification, and the maximum PH₃ adsorption capacity of 253 mg/g can be realized based on well prepared KOH-AC with modification of 2.5% Cu. It seems that the activated carbon produced from chemical activation of tobacco stem would be an effective and alternative adsorbent for PH₃ adsorption because of its high surface area, adsorption capacity, and low cost.     

Preparation and Phosphine Adsorption of Activated Carbon Prepared from Walnut Shells by KOH Chemical Activation

Walnut-shell activated carbons (WSACs) with high surface area and predominant micropore development were prepared by KOH chemical activation. The effects of carbonization temperature, activation temperature, and ratio of KOH to chars on the pore development of WSACs and PH₃ adsorption performance of the modified walnut-shell activated carbons (MWSACs) were studied. Criteria for determining the optimum preparation conditions were pore development of WSACs and PH₃ breakthrough adsorption capacity of MWSAC adsorbents. The result shows that the optimum preparation conditions are a carbonization temperature of 700°C, an activation temperature of 700°C, and a mass ratio of 3. The BET surface area and the micropore volume of the optimal WASC are 1636m²/g and 0.641cm³/g, respectively. The micropore volume percentage of WSAC plays an important role in PH₃ adsorption when there is a slight difference in BET surface areas. High-surface-area WSACs with predominant micropores are suitable for PH₃ adsorption removal. The MWSAC adsorbent owns the biggest PH₃ breakthrough adsorption capacity (284.12mg/g) due to the biggest specific surface area, total pore volume, and micropore volume percentage. The MWSAC adsorbent will be a potential adsorbent for PH₃ adsorption removal from yellow phosphorus tail gas.     

Effects of chemical modification of petroleum cokes on the properties of the resulting activated carbon

Activated carbons have been prepared from petroleum cokes by the combination of a chemical treatment with HClO₄ or H₂O₂ and a chemical activation with KOH at a constant KOH/coke ratio of 3/1. The influence of different chemical treatments on the properties of the activated carbon precursors and final carbons activated with KOH was invested by using XRD, FTIR, and BET techniques. XRD results indicated that the value of interplanar distance d₀₀₂ increased by chemical treatment and the disappearance of the peak corresponding to 0 0 2 faces correlated to high specific surface area. FTIR studies showed that chemical modification promoted the formation of surface oxygen functionalities. Significant effects on BET surface area, pore texture and iodine adsorption capacity were evidenced. The results show that chemical modification prior to activation dramatically increased the BET surface area and total pore volume of the resulting activated carbon. Modified petroleum coke based activated carbon with chemical activation had higher specific surface area (2336 m²/g) and better iodine adsorption value (1998 mg/g).     

Activated carbon produced from Sasol-Lurgi gasifier pitch and its application as electrodes in supercapacitors

A pyrolysis product derived from Sasol-Lurgi gasifier pitch was activated using different proportions of KOH. The increase of the amount of KOH used for activation caused the activation degree of the carbons to increase very significantly. The activated carbons obtained using lower amounts of KOH were mainly microporous, while the amount of mesopores developed in the samples progressively increased for the carbons activated with higher proportions of KOH. The gravimetric specific capacitance of samples obtained with (2:1), (3:1) and (5:1) KOH to carbon ratio were rather similar at low current densities (∼400 F/g at low current densities), despite the significant differences observed in their textural characteristics. Supercapacitors built with the activated carbons obtained with (2:1) and (3:1) KOH to carbon ratio yielded the highest volumetric capacitance (higher than 200 F/cm³ at low current densities), while the most activated sample yielded the lowest values, due to the significant reduction in density caused by activation. The high values of capacitance observed result from the combination of two mechanisms of energy storage: double layer formation and pseudocapacitance.     

Lead adsorption on brown coal activated with potassium hydroxide

The adsorption of lead ions (from an aqueous solution of Pb(AcO)₂) by activated carbons based on brown coal from the Aleksandriisk deposit (Ukraine) was studied. The activated carbons were prepared by the heating (800°C; 1 h) of coal impregnated with potassium hydroxide at KOH/coal weight ratios to 2 g/g. The kinetics of the process was studied, and the adsorption isotherms of Pb²⁺ ions were obtained in the region of initial salt concentrations of 0.001–0.1 mol/dm³. The adsorption data were compared with the adsorption capacity of an OU-B commercial adsorbent.     

Synthesis of activated carbons by chemical activation of new anthracene oil-based pitches and their optimization by response surface methodology

This paper deals with the synthesis of new anthracene oil-based activated carbons by chemical activation with KOH. It focuses on the optimization of the processing conditions involved by means of surface response methodology. A factorial design (2³+3) in one block with four degrees of freedom was used to optimize the process, based on the responses BET surface area, total pore volume, mesopore volume, micropore volume and mol ratio CO:CO₂. The variables measured include KOH to pitch ratio (1:1, 3:1 and 5:1), activation temperature (700 up to 1000 °C) and pitch characteristics. The activation of anthracene oil-based pitch led to activated carbons with BET surface area values of 2880 m² g⁻¹. The factorial design expresses every response factor as a mathematical equation using the experimental variables. The most critical factor for each experiment design response has been identified from the analysis of variance (ANOVA). These mathematical models were also used to obtain the optimum processing conditions for the production of activated carbon with controlled properties. The experimental processing of the optimized activated carbons gave rise to a sample with BET, total pore volume, mesopore volume, micropore volume values which were in good agreement with those predicted by statistical analysis.     

Porous structure and adsorptive properties of pineapple peel based activated carbons prepared via microwave assisted KOH and K2CO3 activation

The present research explores the feasibility of microwave irradiation for preparation of high surface area activated carbon from pineapple peel (PPAC), an agricultural effluent emitted from the food can processing industries via KOH and K₂CO₃ activation. The activation process was performed at the microwave power of 600 W and irradiation time of 6 min. The equilibrium behavior of PPAC was investigated by performing batch adsorption experiments using methylene blue as adsorbate. Nonlinear adsorption isotherm models, Langmuir, Freundlich and Temkin were used to simulate the equilibrium data. KOH activated sample demonstrated a better development of pore structure, with the BET surface area, total pore volume and average pore size of 1006 m²/g, 0.59 m³/g and 23.44 Å, respectively, while the monolayer adsorption capacity of methylene blue was determined to be 462.10 mg/g. The findings support the potential use of microwave assisted KOH and K₂CO₃ activation as a promising activation technique.     

Chemically activated fungi-based porous carbons for hydrogen storage

A set of porous carbons has been prepared by chemical activation of various fungi-based chars with KOH. The resulting carbon materials have high surface areas (1600–2500 m²/g) and pore volumes (0.80–1.56 cm³/g), regardless of the char precursors. The porosities mainly derived from micropores in activated carbons strongly depend on the activation parameters (temperature and KOH amount). All activated carbons have uniform micropores with pore size of 0.8–0.9 nm, but some have a second set of micropores (1.3–1.4 nm pore size), further broadened to 1.9–2.1 nm as a result of increasing either the activation temperature to 750 °C or KOH/char mass ratio to 5/1. These fungi-based porous carbons achieve an excellent H₂ uptake of up to 2.4 wt% at 1 bar and −196 °C, being in agreement with results from other porous carbonaceous adsorbents reported in the literature. At high pressure (ca. 35 bar), the saturated H₂ uptake reaches 4.2–4.7 wt% at −196 °C for these fungi-based porous carbons. The results imply a great potential of these fungi-based porous carbons as H₂ on-board storage media.     

Preparation of activated carbon derived from Jatropha curcas fruit shell by simple thermo-chemical activation and characterization of their physico-chemical properties

High surface area activated carbons were prepared by simple thermo-chemical activation of Jatropha curcas fruit shell with NaOH as a chemical activating agent. The effects of the preparation variables, which were impregnation ratio (NaOH:char), activation temperature and activation time, on the adsorption capacity of iodine and methylene blue solution were investigated. The activated carbon which had the highest iodine and methylene blue numbers was obtained by these conditions as follows: 4:1 (w/w) NaOH to char ratio, 800 °C activation temperature and 120 min activation time. Characterization of the activated carbon obtained was performed by using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and nitrogen adsorption isotherm as BET. The results present that the activated carbon possesses a large apparent surface area (S_BET = 1873 m²/g) and high total pore volume (1.312 cm³/g) with average pore size diameter of 28.0 Å.     

Isotropic petroleum pitch as a carbon precursor for the preparation of activated carbons by KOH activation

Results show that it is possible to activate a low softening point isotropic petroleum pitch, without intermediate pre-treatments, by chemical activation with KOH. The chemical activation is carried out by direct heat treatment of a mixture of the isotropic pitch and KOH. It produces activated carbons (ACs) with micropore volumes as high as 1.12 cm³/g, and BET surface areas around 3000 m²/g. The activating agent/precursor ratios studied (from 1/1 to 4/1; wt./wt.) show, as expected, that increasing the ratio enhances the adsorption characteristics of the resulting AC.     

Hierarchical porous carbons with controlled micropores and mesopores for supercapacitor electrode materials

Various porous carbons were prepared by CO₂ activation of ordered mesoporous carbons and used as electrode materials for supercapacitor. The structures were characterized by using X-ray diffraction, transmission electron microscopy and nitrogen sorption at 77 K. The effects of CO₂ treatment on their pore structures were discussed. Compared to the pristine mesoporous carbons, the samples subjected to CO₂ treatment exhibited remarkable improvement in textural properties. The electrochemical measurement in 6 M KOH electrolyte showed that CO₂ activation leads to better capacitive performances. The carbon CS15A6, which was obtained after CO₂ treatment for 6 h at 950 °C using CMK-3 as the precursor, showed the best electrochemical behavior with a specific gravimetric capacitance of 223 F/g and volumetric capacitance of 54 F/cm³ at a scan rate of 2 mV/s and 73% retained ratio at 50 mV/s. The good capacitive behavior of CS15A6 may be attributed to the hierarchical pore structure (abundant micropores and interconnected mesopores with the size of 3-4 nm), high surface area (2749 m²/g), large pore volume (2.09 cm³/g), as well as well-balanced microporosity and mesoporosity.     

Resorcinol-formaldehyde based porous carbon as an electrode material for supercapacitors

Porous carbon materials were prepared using resorcinol and formaldehyde catalyzed by KOH in a sol-gel process followed by carbonization, during which the KOH serves as an activating agent and generates pores mainly located in the micropore range. With an increase of mass ratio of KOH to resorcinol from 1 to 4, both the specific surface area and the pore volume of the carbons increased, from 522 to 2760 m²/g and 0.304 to 1.347 cm³/g, respectively, but the average pore diameter decreased from 4.4 to 2.5 nm. Samples were investigated as electrode materials in supercapacitors and the relevant electrochemical behavior was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and constant current charge-discharge experiments using 30% KOH aqueous solution as electrolyte. The highest specific capacitance of up to 294 F/g was obtained at a current density 1 mA/cm² for the sample with mass ratio of KOH to resorcinol of 2. Only a slight decrease in capacitance for the same sample, from 294 to 242 F/g, was observed when the current density increased from 1 to 30 mA/cm². The specific capacitance only decayed 3% at a current density 30 mA/cm² after 1000 cycles, which indicates that the sample possesses excellent power property and cycle durability.     

Highly mesoporous carbonaceous material of activated carbon beads for electric double layer capacitor

The activated carbon beads (ACB) are prepared by a new preparation method, which is proposed by mixing the coal tar pitch and fumed silica powder at a certain weight ratio and activation by KOH at different weight ratios and different temperatures. The BET surface area, pore volume and average pore size are obtained based on the nitrogen adsorption isotherms at 77 K by using ASAP 2010 apparatus. The results show that our samples have much high specific surface area (SSA) of 3537 m² g⁻¹and high pore volume value of 3.05 cm³ g⁻¹. The percentage of mesopore volume increases with the weight ratio of KOH/ACB ranging from 4% to 72%. The electrochemical double layer capacitors (EDLCs) are assembled with resultant carbon electrode and electrolyte of 1 mol L⁻¹ Et₄NBF₄/PC. The specific capacitance of the ACB sample could be as high as 191.7 F g⁻¹ by constant current charge/discharge technique, indicating that the ACB presents good characteristics prepared by the method proposed in this work. The investigation of influence of carbon porosity structure on capacitance indicates that the SSA plays an important role on the capacitance and all the pore sizes of less than 1 nm, from 1 to 2 nm and larger than 2 nm contribute to the capacitance. Mesopore structure is beneficial for the performance at high current density.     

Molded micro- and mesoporous carbon/silica composite from rice husk and beet sugar

A molded carbon/silica composite with high micro- and mesoporosity, as well as a high bulk density, was fabricated by activating a disk-molded precursor made from carbonized rice husk (RH) and beet sugar (BS) at 875 °C in CO₂. The pore structure of the RH- and BS-based carbon/silica composite (RBC) was analysed in relation to the bulk density. An activation time of 2.0 h provided the largest BET specific surface area (1027 m²/g) and total pore volume (0.68 cm³/g) and a low bulk density (0.54 g/cm³). An RBC that was first activated for 1 h was immersed again in BS syrup and then activated in CO₂ for 1 h. This two-step activation process provided both a high bulk density (0.69 g/cm³) and a highly textured structure (BET specific surface area, 943 m²/g; total pore volume, 0.56 cm³/g). The immersion in BS syrup was useful for improving the texture without reducing the bulk density, in comparison to one-step activation for 1.0 h. The suspension of the RBCs was basic because of the residual inorganic compounds of potassium and calcium. However, the basicity of the suspension was alleviated by washing the RBCs with water.